docs: def K_tilting_disk_check_valve_Crane(D, angle, fd=None):
      r'''Returns the loss coefficient for a tilting disk check valve as shown in
      [1]_. Results are specified in [1]_ to be for the disk's resting position
      to be at 5 or 25 degrees to the flow direction.  The model is implemented
      here so as to switch to the higher loss 15 degree coefficients at 10 
      degrees, and use the lesser coefficients for any angle under 10 degrees.
          
      .. math::
          K = N\cdot f_d
          
      N is obtained from the following table:
  
      +--------+-------------+-------------+
      |        | angle = 5 ° | angle = 15° |
      +========+=============+=============+
      | 2-8"   | 40          | 120         |
      +--------+-------------+-------------+
      | 10-14" | 30          | 90          |
      +--------+-------------+-------------+
      | 16-48" | 20          | 60          |
      +--------+-------------+-------------+
      
      The actual change of coefficients happen at <= 9" and <= 15".
              
      Parameters
      ----------
      D : float
          Diameter of the pipe section the valve in mounted in; the
          same as the line size [m]
      angle : float
          Angle of the tilting disk to the flow direction; nominally 5 or 15
          degrees [degrees]
      fd : float, optional
          Darcy friction factor calculated for the actual pipe flow in clean 
          steel (roughness = 0.0018 inch) in the fully developed turbulent 
          region; do not specify this to use the original Crane friction factor!,
          [-]
          
      Returns
      -------
      K : float
          Loss coefficient with respect to the pipe inside diameter [-]
  
      Notes
      -----    
      This method is not valid in the laminar regime and the pressure drop will
      be underestimated in those conditions.
  
      Examples
      --------
      >>> K_tilting_disk_check_valve_Crane(.01, 5)
      1.1626516551826345
      
      References
      ----------
      .. [1] Crane Co. Flow of Fluids Through Valves, Fittings, and Pipe. Crane,
         2009.
      '''
      if fd is None:
          fd = ft_Crane(D)
      if angle < 10:
          # 5 degree case
          if D <= 0.2286:
              # 2-8 inches, split at 9 inch
              return 40*fd
          elif D <= 0.381:
              # 10-14 inches, split at 15 inch
              return 30*fd
          else:
              # 16-18 inches
              return 20*fd
      else:
          # 15 degree case
          if D < 0.2286:
              # 2-8 inches
              return 120*fd
          elif D < 0.381:
              # 10-14 inches
              return 90*fd
          else:
              # 16-18 inches
              return 60*fd